Many metal machining processes require the distribution of cooling fluid at a cutting tool edge in order to cool the tool, lubricate the cutting edge, remove metal chips from deep holes and, in some instances, to gauge the size of a machined feature. An effective and industry-proven method of applying such cooling fluid is through the use of a rotating fluid union. Unions which incorporate a rotating fluid seal between a pair of relatively rotating parts are well known in this field of the art. A leak tight connection is provided between the fluid supply and the cutting tool edge as the rotating union allows the passage of cooling fluid to the center of the spindle, the center of the cutting tool and directly to the cutting tool edge.
Typically, a rotary union includes a rotating seal member which is positioned in concentric relation to a stationary seal member within a single common housing. Means are provided to bias the two seal members against one and other such that their respective axial seal faces are in fluid-tight engagement. The rotating seal member is journaled on a bearing for rotation relative to both the stationary seal member and the single common housing and further includes a shaft which extends from the housing to be securely inserted within the rotating spindle for rotation therewith.
The standard mechanical ball bearing rotary union has proven to provide satisfactory service at relatively low rotational speeds, i.e. .ltoreq.4,000 rpm, and at relatively low or moderate pressures. However, these types of unions often experience operational problems when an attempt is made to use them at relatively high rotational speeds, i.e. .gtoreq.5,000 rpm, or at high pressures.
Various machining applications today require that a rotating union provide a reliable leak tight connection at high rotational speeds, i.e. approximately 10,000 rpm, and at coolant pressures upwards of 1,000 psi. Such high-production metal cutting machines are often employed in transfer lines and are used, for example, in the production of detailed components such as transmissions, engine blocks, cylinder heads, etc. The reliability of the rotating union is of critical importance in maintaining high production rates and machine "up-time."
Standard rotating unions have many shortcomings which adversely affect their overall reliability. Factors which must be considered in their application include: 1) A flexible hose connection is usually required between the stationary fluid supply and the rotating union to prevent undue loading upon the ball bearings. 2) An extremely accurate connection between the rotating union and the spindle is necessary to prevent vibration and wobble. If a connection is worn or damaged the entire union may vibrate, affecting not only union performance but also the accuracy and finish of the cutting tool. Short service life or catastrophic failure, such as a broken union sleeve, may result from such harmonic vibrations. 3) Advances in tooling and increased production rates necessarily require an increase in both speed and pressure. Bearing life has thus become an increasing problem. 4) Bearings are highly susceptible to grease contamination and wash-out from the splash or mist effect from the flow of cooling fluid.
A relatively recent development is a "bearingless" coolant union as shown, for example, in U.S. Pat. No. 5,174,614, issued Dec. 29, 1992 to Kaleniecki and entitled "Bearingless Rotary Mechanical Fluid Coupling." This union is intended to be rigidly mounted to the frame of a machine's spindle by means of a mounting adapter. Rigid mounting of the rotary union eliminated the need for bearings within the housing assembly as the rotor assembly is allowed to rotate freely with the spindle. Rigid mounting also allows the rotating union to be plumbed solid with the stationary machine. Loads from the plumbing connection are transferred directly to the machine's frame by means of a mounting adapter. Vibration is reduced as the only rotating member of the union is the sleeve which is supported by the machine's spindle bearings.
This early design of a bearingless coolant union eliminated some of the common causes of premature rotating union failure and thereby increased the union's reliability. However, there are still a variety of shortcomings associated with this particular bearingless design. Such bearingless unions are essentially "two-piece" devices; the first piece intended to rotate with a spindle and having a rotating seal, and the second piece intended to remain stationary and including a stationary seal. Prior to installation, both of these precision lapped seals are exposed to the environment and are susceptible to damage. Proper installation procedure requires not only a thorough cleaning and oiling of the seal faces, but also that exacting alignment steps be taken, often requiring the shimming of the union, to position the two pieces within the union's allowable set-up dimensions.
What is needed in this field of art is a unitary, bearingless fluid union which allows its rotor member to rotate freely with a machine's spindle, whose seals remain in constant fluid-tight abutment, and which features a simplified installation process which does not require the cleaning or alignment of its seal faces.